Even with Earth Power, I wouldn't send this poor Sea critter out against an Electric-type. Lose Earth Power for Surf, seeing as its the only reliable STAB, and with Corsola's terrible Speed stat, it's not like it'll get to move before most Electric-types, anyway. It'll be outsped by everything, and just picked off with a STAB Thunderbolt.
Also, Corsala's Special Defense is good enough to do with Light Screen. Recover would be more useful, in the long run. Most opponents you will will face will go down to Ice Beam just as easily as Power Gem, so replace Power Gem with something for survival, such as Aqua Ring.
Now just put Leftovers on it, and you've a Pokemon BUILT to survive against the toughest of opponents (That cannot 0HKO it).